This invention relates to a light-emitting liquid crystal display device having a backside illuminator. More particularly, this invention relates to such device wherein the backside illuminator includes light-emitting sites in registration with pixels of a liquid crystal panel.
A typical liquid crystal display device forms a display that is viewed through a front side and features an array of pixels, each of which has a bright or dark appearance. The device includes a liquid crystal panel comprising a layer of liquid crystal material sandwiched between front and back transparent polymer or glass plates and between front and back polarizers having perpendicular axis of polarization. The pixels are defined by transparent electrodes adjacent the liquid crystal layer. Light illuminating the back side of the panel is filtered by the back polarizer to admit only polarized light. In the absence of an applied electrical field, the polarized light is re-oriented by the liquid crystal layer to pass through the front polarizer, thereby creating a bright pixel for the display. However, an electrical potential applied between the electrodes alters the intermediate liquid crystal material to prevent the polarized light from passing through the front polarizer, thereby creating a dark pixel. Thus, by selectively applying electrical current to the electrodes, the pixel is switchable between a transparent or bright state and an opaque or dark state.
In addition to the pixels, the display also includes a matrix area. As used herein, matrix refers to the area that surrounds the pixel and separates the pixel from adjacent pixels. The matrix is mainly derived from spacing that is required to electrically isolate the electrodes that define the pixel. In a typical display comprising an array of pixels, the matrix appears as intersecting lines interposed between rows and columns of pixels.
While the liquid crystal panel creates a display by altering the light transmission properties of the pixels, the liquid crystal panel does not generate the light for the display. Thus, the device requires a separate light source. In a backlit device of the type to which this invention relates, the back side of the liquid crystal panel is illuminated by light from an electric light source, such as a light bulb or a light-emitting diode. It is known to utilize a light panel to distribute light and avoid hot spots in the display. Light from the light source is directed into the light panel, typically at an edge, and is emitted from a face toward the back side of the liquid crystal panel. The back of the light panel may include irregularities, for example, bumps or dimples, to disperse the light through the front face. In designing a light panel, heretofore, it has been a common desire to provide a diffuse light to uniformly illuminate the liquid crystal panel, including both pixels and matrix.
Whereas it is desired to minimize the thickness of the display device, light panels designed for diffuse light contribute significantly to the total thickness. Also, because the light source in portable devices is powered by a battery, it is desired to minimize the power requirements for the light source and thereby extend operating time, while providing adequate light to assure pixels of sufficient brightness to allow the display to be readily discerned. However, a significant amount of light irradiates the matrix and is not utilized in forming the display. In addition, diffuse rays irradiate the liquid crystal panel at varying angles, thereby blurring the perimeters of the pixels and reducing resolution of the display.